As used herein, the term “magnetic field sensing element” is used to describe a variety of electronic elements that can sense a magnetic field. One such magnetic field sensing element is a magnetoresistance (MR) element. The magnetoresistance element has a resistance that changes in relation to a magnetic field experienced by the magnetoresistance element.
As is known, there are different types of magnetoresistance elements, for example, a semiconductor magnetoresistance element such as Indium Antimonide (InSb), a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), and a tunneling magnetoresistance (TMR) element, also called a magnetic tunnel junction (MTJ) element.
Of these magnetoresistance elements, the GMR and the TMR elements operate with spin electronics (i.e., electron spins) where the resistance is related to the magnetic orientation of different magnetic layers separated by nonmagnetic layers. In spin valve configurations, the resistance is related to an angular direction of a magnetization in a so-called “free-layer” respective to another layer so-called “reference layer.” The free layer and the reference layer are described more fully below.
The magnetoresistance element may be a single element or, alternatively, may include two or more magnetoresistance elements arranged in various configurations, e.g., a half bridge or full (Wheatstone) bridge.
As used herein, the term “magnetic field sensor” is used to describe a circuit that uses a magnetic field sensing element, generally in combination with other circuits. In a typical magnetic field sensor, the magnetic field sensing element and the other circuits can be integrated upon a common substrate.
Magnetic field sensors are used in a variety of applications, including, but not limited to, an angle sensor that senses an angle of a direction of a magnetic field, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet or a ferromagnetic target (e.g., gear teeth) where the magnetic field sensor is used in combination with a back-biased or other magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.
Various parameters characterize the performance of magnetic field sensors and magnetic field sensing elements. With regard to magnetic field sensing elements, the parameters include sensitivity, which is the change in the output signal of a magnetic field sensing element in response to a magnetic field, and linearity, which is the degree to which the output signal of a magnetic field sensor varies linearly (i.e., in direct proportion) to the magnetic field.
GMR and TMR elements are known to have a relatively high sensitivity, compared, for example, to Hall elements. GMR and TMR elements are also known to have moderately good linearity, but over a restricted range of magnetic fields, more restricted in range than a range over which a Hall element can operate. However, it is known that even in the restricted range of magnetic fields, the linearity of the GMR or TMR element suffers from irregularities. Also, it is known that some GMR and TMR elements tend to change behavior after high temperature storage. Thus, it would be desirable to provide a GMR or a TMR element for which linearity irregularities are reduced and for which high temperature storage has a reduced effect.
Conventional GMR and TMR elements, and, in particular, spin valves, are known to also have an undesirable hysteresis behavior, which reduces their accuracy of magnetic field or current measurements. Thus, it would also be desirable to provide a GMR or TMR element with reduced hysteresis.
Conventional double pinned GMR and TMR elements and, in particular, spin valves, that have two pinning layers comprised of PtMn, are known to be difficult to anneal to two different annealed directions, e.g., two directions that are ninety degrees apart.